This invention relates generally to control methods to prevent engine, transmission and ancillary device overspeed in vehicles having an internal combustion engine mechanically connected to the wheels or tracks of the vehicle and more particularly to sequences of steps initiated automatically by electronic control modules to prohibit damage due to operator error or component failure.
Modern heavy duty trucks and heavy duty off-road mining and construction equipment have engines and drivetrains which are susceptible to extensive and expensive damage when operated in excess of about 2500 to 3000 RPM (crankshaft revolutions per minute), depending upon design. High-pressure hydraulic pumps, especially variable output pumps, are similarly speed limited. The advent of electronic engine controls allows engine RPM to be controlled by interrupting ignition pulses in Otto cycle engine and by limiting fuel flow in Diesel cycle engines. Neither approach prevents overspeed when a vehicle is in a gear and the weight of the load creates momentum sufficient to backload through the transmission and force the engine speed above the critical limit.
U.S. Pat. No. 5,587,905 to Yesel et al., granted Dec. 24, 1996, discloses a system for preventing overspeed in heavy equipment having an electronically controlled transmission and engine by disallowing downshifting the transmission to the desired gear as engine and transmission speeds allow. A microprocessor-based electronic module serves as a controller which compares various input signals to stored benchmarks and responds in a predetermined pattern.
U.S. Pat. No. 5,416,698 to Hutchison, granted May 16, 1995, is directed to a warning system to advise a vehicle operator that a gear has been selected which will cause overspeeding or underspeeding of the engine when the clutch is re-engaged.
U.S. Pat. No. 4,463,842 to Redzinski, granted Aug. 7, 1984, discloses an automatic lockup of a torque converter in the driveline of a work vehicle responsive to the speed of the output shaft of a torque converter.
U.S. Pat. No. 5,615,653 to Faletti et al., granted Apr. 1, 1997, is representative of compression release engine braking technology frequently employed on Diesel engines for freight hauling.
The prior art addresses individual aspects for avoiding gear selection errors and smoothing techniques for cruise control systems. None of the prior art is directed to unified systems to protect engines, pumps and ancillaries from overspeed when a combination of weight, slope and mechanical coupling of engine and drivetrain produce a potentially damaging overspeed through backloading.
The present invention is directed to overcoming one or more of the problems or disadvantages associated with the prior art.
The invention is directed to systems for the protection of components of a heavy vehicle from damage due to overspeed of the engine and engine driven components.
In a first aspect of the invention, a system is provided to override the operator""s manual control of the gear selection in a transmission having electronic shifting control. In a second aspect of the invention, there is provided a system to disengage a lockup clutch of a torque converter when a potential overspeed condition is identified in an output from the transmission.
In another aspect of the invention, there is provided a system to slow and optionally retard an engine approaching an overspeed condition by overriding an operator-selected engine speed control and by optionally phasing in a compression release engine braking system.
In a further aspect of the invention, a system is provided to destroke variable capacity hydraulic pumps associated with the engine in response to the same signals provoking a system for the override of the operator-selected engine speed.
In yet another aspect of the invention, the control functions for transmission control, torque converter control, engine control and pump destroking are controlled by a microprocessor which also transmits visual/or and auditory messages to the operator, records operating events and allows operator override in the event of the failure of other systems on the vehicle.